This invention relates to fluid flow controls and is concerned particularly with improvements in check valves of the type having a valve element in the form of a flexible disk mounted adjacent the valve seat. The valve element and seat are arranged so that a pressure differential in one direction will press the disk into sealing relation with the seat while a pressure differential in the opposite direction will flex the disk to permit fluid to flow past it, to and through the valve outlet. A commercially available valve of this type is described in U.S. Pat. No. 3,889,710 to Borst. The device described in that patent includes a housing which defines a valve chamber having generally opposed inlet and outlet passageways. A concave seating surface surrounds the inlet passageway within the valve chamber. A normally flat elastomeric disk valve is located in generally facing relation to the concave seating surface and is biased toward and against the concave seating surface by an abutment structure which bears against the central region of the disk thereby maintaining the periphery of the disk in sealing contact with the concave seating surface. Increased fluid pressure against the downstream face of the disk increases the sealing engagement with the seating surface. Increased pressure on the upstream face of the disk causes it to flex to a more dished configuration, bending further about the abutment structure and breaking the seal of the seating surface to allow fluid to flow around the periphery of the disk to the outlet passageway.
The device described in Borst U.S. Pat. No. 3,889,710, although usable in situations where a high degree of precision is not required, and where flow rates and pressure differentials are at moderate levels, presents a number of difficulties when used in high precision environments. It also presents difficulties when used with relatively high flow rates and pressure differentials as well as with relatively low flow rates and pressure differentials. For example, when used in relatively high flow rate applications the valve displays a tendency to build up substantial back pressures. When used in applications calling for relatively low flow rates and low pressure differentials, the Borst valve displays variations in its operating characteristics. For example, a significant feature of the valve described in the Borst patent relates to the ability of the valve disk to shift about within the valve housing. The degree to which the disk is permitted to shift about tends to change the operating characteristics of the valve as the disk shifts to various positions in the housing. For example, the cracking pressure of the valve may change somewhat from time to time as the valve operates. While this may be an acceptable feature where critical applications and precise operation is not essential, it presents a number of difficulties when precise operation is required. This difficulty is magnified particularly in applications calling for low pressure differentials and low flow rates.
Another difficulty presented by the Borst valve is that it is difficult to manufacture such valves with repeated precise control over the cracking pressure of the valve (i.e., the pressure at which the valve shifts from its closed to its open position). The Borst type of valve tends to display significant variations from valve to valve which, in low pressure relatively delicate systems may be intolerable and result in unreliable operation of the system which the valve is meant to control.
Another disadvantage with the Borst type of valve is that, once manufactured, it is operable only at a single pressure level and cannot be accommodated to varied conditions and flow parameters. Thus, should a different cracking pressure of other variation in operating characteristics be required the valve must be replaced in its entirety.
The operating characteristics of the Borst valve are determined by the internal configuration of the valve housing and its cooperation with the valve element. Thus another problem with the valve is that its manufacture is highly sensitive to varying manufacturing conditions and, therefore, necessarily results in relatively high manufacturing costs to monitor and control those conditions.
Still another difficulty presented with the Borst type of valve is that it does not have as rapid a response, particularly in relatively low flow rate and low pressure differential situation with the result that the valve may not act as quickly as desired.
It is among the general objects of the invention to provide a disk check valve which overcomes the foregoing and other difficulties.